Standing on the Edge of the Event Horizon
by DaLiza
Summary: Fitz asks Mack for relationship advice. Set during the second half of season three. Third chapter added by request.
1. Chapter 1

Fitz walked into the hangar at S.H.I.E.L.D. headquarters, hoping to find Mack. At first glance, the hangar seemed deserted, but soon Fitz spotted the mechanic bent over the quinjet's engine. As Fitz approached him, he started having second thoughts. He considered Mack a friend, someone he trusted, but was this really a topic he should discuss with him? What if it made things awkward between them? He didn't have many people in his life who he could call friends; he couldn't afford to lose one.

Fitz had turned around to leave the hangar when Mack saw him. "Hey, Fitz." Mack put down his tools and smiled at the engineer. "What are you doing here?"

"I was going to talk to you about something...but it's not important. You look like you're busy. I'll see you later." He started to walk away.

"Hold on, Turbo," Mack said. "I was busy, but I could use a break." He picked up a rag and wiped the sweat from his brow. "What's on your mind?"

Fitz looked away as he contemplated his response. Should he tell Mack the truth? Or was it better to lie? Would Mack know if he was lying?

Eventually Mack broke the silence. "Okay. You don't have to tell me. I think I know."

Fitz shifted his weight from one foot to another. "You do?"

"You and Simmons are finally dating."

"How did you know?" Fitz's cheeks reddened. He had thought that he and Jemma were being discreet about the change in their relationship.

Mack grinned. "You used to try to play it cool, but now you smile whenever she walks into the room. I'm happy for you, Fitz. It's been a long time coming."

"Thanks. Simmons and I have been getting closer, and it's been great. Really great. But..."

"But what?"

"I'm worried about what happens when our relationship becomes…" Fitz lowered his head, not wanting to meet Mack's eyes. "...more physical."

"What? Because S.H.I.E.L.D. regulations say you can't have a romantic relationship with a fellow agent?" Mack laughed. "Coulson won't stop you. No one will. Everyone is rooting for you two. And I mean _everyone_. I can't tell you how many times I've overheard agents tell each other that they 'ship FitzSimmons.'"

"They _ship_ us? W-What does that mean?" Fitz asked.

"It means that they want you two to get together. I know at least a couple agents have placed bets on when it will happen."

"You're serious?"

"Completely serious."

"I didn't know that there were so many people who cared about our personal lives."

"Why wouldn't they? From what I've heard, you and Simmons were legends at the Academy. A lot of people look up to you guys and want you to be happy. If Bobbi and Hunter were here, they'd be thrilled. You and Simmons have something special, something some people spend their whole lives searching for. Don't let regulations stand in your way."

"We won't. That's not what I'm worried about."

"Okay. Then...what's the problem?"

Fitz took a deep breath, then let it out slowly. "Jemma had boyfriends at the Academy. And she had Will. She has experience in being intimate. But I never had the opportunity to...gain experience."

"You're saying that you've never…oh. Wow."

Fitz wrapped his arms around himself. "I'm sorry. I shouldn't have told you that. I knew it would make things weird." He started to walk away again.

"Fitz, wait! You didn't do anything wrong. I was just...surprised, that's all. But it makes sense. You were a child genius at the head of your class; you couldn't have had much time for dating."

"Yeah. I spent a lot of time alone as a kid. There were a few girls in school that I liked, but none of them liked me back. They thought I was too brainy, too weird. Jemma was the first person in my life who understood me. She's the first person I can imagine having a relationship with...the first person I can imagine having a future with. So I don't want to disappoint her. I was thinking that…if it's not too awkward...maybe you could give me some advice...so I won't be bad at it."

Mack was quiet for several seconds. "You know those scenes in TV shows and movies where a couple falls into bed and everything is romantic and perfect?"

"Yes."

"Don't expect your first time to be like that. Getting to know someone in that way...it's going to be a little awkward and embarrassing at first. You'll be nervous and she might be too. Be honest with her and you'll figure it out together; you always do. You'll be alright, Turbo. Just give it time."

Fitz nodded. "Thanks, Mack."

As Mack patted Fitz on the shoulder, he heard footsteps behind him. "That must be Agent Simmons."

"How did you know?" Asked Simmons as she approached the two men.

"Fitz's smile," answered Mack, turning to face her. "I'll let you two talk. I should get back to work." He picked up his tools and returned to the quinjet's engine.

"Do you need me in the lab?" Fitz asked the woman he loved.

"No, we're still waiting on test results. I was about to eat lunch and I wondered if you wanted to join me."

"I'd love to," Fitz said, impulsively kissing her cheek.

"Fitz!" Simmons blushed and took a step back. She stole a glance at Mack, who was trying to pretend he hadn't seen anything. "I thought we agreed to be _discreet_ in front of our colleagues."

"I know, but Mack already figured it out and I haven't been able to kiss you all day." He took her hands in his. "Will you forgive me?"

Simmons sighed. How could she stay mad at Fitz when he looked at her like she was the most important person in the universe? She closed the distance between them. "Always."

Hand in hand, the smiling scientists left the hangar together.

* * *

 **Thanks for reading! All comments are greatly appreciated.**


	2. Chapter 2

**Four Months Later**

Fitz walked into the hangar at S.H.I.E.L.D. headquarters, hoping to find Mack. When he spotted his friend doing repairs on Zephyr One, Fitz smiled and rushed to his side.

"Someone's in a good mood," Mack said when he looked up from the engine and noticed Fitz's expression. "Did your soccer...football...whatever you call it...team win a championship?"

Fitz laughed. "No, it wasn't even close. But that doesn't matter now. I need to ask you something."

"Is this about..." Mack lowered his voice, even though there was no one else in the hangar. "...the thing we talked about a few months ago? Because I'm not comfortable going into more detail about that. I'm sure there are plenty of books or websites you could…well, you should probably stay away from that kind of website because Daisy could access your search history…"

"Relax, Mack, I don't need any more advice about..." Fitz blushed. "...being intimate." He and Jemma had figured it out together, just as Mack had predicted they would.

"That's good to hear." Mack's look of concern was quickly replaced by a smile. "So what do you need?"

"Jemma and I are getting married, so I need a best man for my wedding. Would you like the job?"

Mack enveloped Fitz in a hug. "That's awesome, Turbo! I would be honored to be your best man."

"Thanks, Mack," Fitz said when Mack released him. "I don't know yet when the wedding will be, or where…possibly England or Scotland so our parents don't have to travel far." Fitz was grinning from ear to ear. "I can't believe it's really happening."

"I can," said Mack. "So how did it go down?"

Fitz sighed. "Not the way I wanted it to. I was planning to propose this weekend. I've been thinking about it for weeks, trying to come up with some clever way to do it. I considered putting a ring inside a miniature TARDIS and saying something like 'Will you be my companion through all of time and space?' But-"

"Hold on a minute. What's a TARDIS?"

"It's the machine the Doctor uses to time travel and visit other planets. But I decided against it because I've given her a bunch of _Doctor Who_ themed birthday presents over the years and I wanted my proposal to be different. Special. So then I considered training a monkey to bring the ring to Jemma-"

"Why am I not surprised?"

"But my Mum talked me out of it. She said she was going to send me my grandmother's wedding ring, and she didn't want to risk anything happening to it. I got the ring in the mail yesterday, and I made a reservation at a nice restaurant, and I was practicing what I would say so it would be perfect. Then Jemma walked in on me. She had told me that she was going to have a late night at the lab, but she finished her paperwork earlier than she expected."

"So she overheard you practicing your speech," Mack said sympathetically.

"Yeah. And she saw the ring in my hand." Fitz's eyes teared up. "She started crying, then she hugged me and said 'yes.'" He lowered his head. "I am happy we're getting married, but I wish I could have given her a nicer proposal."

Mack put a hand on Fitz's shoulder. "Don't be too hard on yourself. What matters is that she said 'yes.' She wants to spend the rest of her life with you. That's no small thing."

"You're right...but maybe I can convince Jemma to let me try it again when we're both dressed up and in a more romantic setting."

"With a monkey," Mack teased.

Fitz started to laugh, but then stopped abruptly. "I could put the ring on a stuffed animal monkey! I know a toy store that has adorable monkey stuffed animals."

"Of course you do."

"Do you want to come with me?" Fitz's eyes were wide with excitement. "You can help me pick one out."

"I don't know, Fitz. I have a lot of work to-"

"Come on, it will be fun! We could get something for you to give to Yo-Yo."

Mack's eyebrows jumped. "You think Yo-Yo wants a stuffed animal?"

"Elena's a beautiful woman, Mack. If _you_ don't buy her a stuffed animal, some other guy will. She'll start dating that guy instead of you, and then one day they'll get married and have three kids and a little fluffy dog-"

Mack laughed and threw his hands up in surrender. "Alright, Turbo. I'll go with you to the toy store, but I need to finish these repairs first."

"Yes!" Fitz gave Mack a high five. "I'll be in the lab. Come find me when you're done."

* * *

A few hours later, Mack finished his work on Zephyr One and went to find Fitz. After a quick look around the lab's various workstations, he saw several scientists he barely knew or didn't know at all, but there was no sign of Fitz. Standing behind one microscope, however, was a scientist he knew very well.

"Simmons," Mack called out as he approached her. "It's good to see a familiar face."

She looked up from the microscope. "It's good to see you too, Mack."

"Fitz asked me to meet him here. Do you know where he is?"

"He ran to the kitchen to grab a snack," Simmons answered. "He should be back any moment now."

"Okay. I'll wait here then." He leaned closer to her and spoke in a low voice. "Fitz told me the news. Congratulations."

Simmons led Mack to a quiet corner of the lab. "Thank you. After everything Fitz and I have been through...it seems rather surreal. I appreciate you agreeing to be Fitz's best man. That means a lot to him."

"It'll be my pleasure. I'm excited for you both."

"The funny thing is that I had been planning to propose to _him_. I was thinking about putting a ring on top of his favorite sandwich, the prosciutto and buffalo mozzarella with a hint of-"

"Pesto aioli," said Mack in unison with Simmons. "I've never seen a man love a sandwich the way Fitz loves that one."

Simmons smiled. "Yes. But then I worried he might ingest the ring before he saw it. I also thought about having a monkey stuffed animal hold it."

"A monkey stuffed animal?" Mack repeated, barely suppressing a laugh.

"I know. It's silly."

Mack shook his head. "No. It's not silly. You two really are perfect for each other."

* * *

 **Thanks for reading! All comments are greatly appreciated.**


	3. Chapter 3

**One Year Later**

Fitz walked into the hangar at S.H.I.E.L.D. headquarters, hoping to find Mack.

"Are you okay, Turbo?" Mack asked when he saw the stunned expression on his friend's face. He put down his tools. "You look like you've seen a ghost."

"I'm...fine," Fitz said slowly, as if he was trying to convince himself. "Just trying to wrap my mind around the fact that my life and Simmons's are going to change forever."

"Really?" Mack sat down on the hangar floor and motioned for Fitz to sit next to him. "So does this mean that you and Simmons are going to be…?"

"Parents." Fitz took a deep breath. "I'm going to be a father, Mack."

Mack hugged his friend. "Congratulations! Does Daisy know yet? Ever since you and Simmons got married, she's been talking about how much she wants you two to have kids. She's convinced that your kids will be geniuses who grow up to save the world."

Fitz laughed. "Simmons is telling Daisy and May. I'm telling you and Coulson."

"I'm excited for you," said Mack. "How are you feeling?"

"I want to be excited...but mostly I'm terrified. I love Simmons and I want to have a child with her, but now that it's actually happening, I'm afraid that I won't be able to protect my family. Maybe if I had powers like Daisy or if I could fight like May...but I can't. If something happened to our child, I...I couldn't live with that."

"Every parent worries about their kids," Mack said, recalling conversations with his cousins about their children. "But I think worrying is a waste of energy; it doesn't stop bad things from happening. All you can do is keep your eyes open and try to be as prepared as you can. You and Simmons will be great parents."

"I'm sure Simmons will be a wonderful mother, but I don't know if I'll be a good father."

Mack was taken aback. "What? Why would you think that?"

Fitz looked down at the floor. "I never had a father. Well, technically I did, but he walked out on my mum when I was still in diapers. And I don't have any siblings, so I don't have much experience with babies."

"My cousin Alex is an only child raised by a single mother, and he felt the same way when his wife was pregnant with their first kid. I remember he called me in a panic a few weeks before she was born, saying he was scared he would screw up his daughter's life and she would hate him. He has three daughters now and they all adore him. He figured it out, and so will you." Mack patted Fitz's shoulder. "Believe me, you're going to be awesome."

Fitz raised his eyes to meet Mack's. "Thanks, Mack. I'm going to miss finding you in the hangar when I need to talk."

"Why would you miss...oh." Mack was silent for several seconds as he realized what Fitz was saying. "You and Simmons are leaving S.H.I.E.L.D.."

"We have to," Fitz said, feeling guilty about abandoning his friends. "Even if we stayed out of the field and in the lab, the lab has been attacked too many times. We can't take any unnecessary risks."

"I understand. You have to do what's best for your kid...especially if he's going to save the world someday."

"Or she," said Fitz. "I'm hoping for a girl, honestly. A mini Simmons who will be as brilliant and courageous as her mother."

"She'd be adorable," agreed Mack. "But a mini Fitz who's a genius engineer like his dad could be pretty cool too."

A smile slowly spread across Fitz's face. "I'm going to be a dad, Mack!"

Mack laughed. "I know, Turbo. I know."

* * *

The goodbye party for Fitz and Simmons was held in the base's common area, which Daisy had decorated with blue and pink balloons. S.H.I.E.L.D. agents were lining up to give the happy couple gifts for the baby. Mack's gift was the biggest of all: a five foot tall monkey stuffed animal with a red bow around its neck.

"That's amazing!" Fitz said, his eyes growing wide when he saw it.

"I got it from Finnegan's," said Mack. Finnegan's was the name of the toy store where Fitz had bought the little monkey stuffed animal he had used to propose to Simmons.

"I'm sure the baby will love it," said Fitz as he took the monkey from Mack's arms.

"Actually, I didn't buy it for the baby; it's for you. I figured you could give it a squeeze whenever you're feeling stressed about parenthood."

Both Fitz and Simmons laughed. "Thanks, Mack," they said in unison.

"I'm going to miss working with you guys," Mack said, giving each of them a hug.

"We'll miss you too," said Simmons. "We hope you'll visit us in Perthshire. The cottage Fitz found for us is really quite lovely."

"I look forward to seeing it. Maybe I can come and babysit every once in a while. Babies love me."

* * *

The first time Mack babysat Eleanor Elizabeth Fitz-Simmons was a disaster. She was six months old and cried the entire time her parents were gone. Mack tried everything he could think of, but nothing he did could soothe her.

When Eleanor was a year old, things went more smoothly. She let Mack give her a bottle and she laughed at the silly faces he made.

When Eleanor was two years old, she started calling him 'Uncle Mack,' a title she never stopped using.

"We're glad to have you in Eleanor's life," Fitz told Mack at his daughter's fifth birthday party. "Don't tell Hunter, but you're her favorite uncle."

"Good to hear," Mack said, smiling. "I can't believe she's five years old now. It seems like yesterday that you were in the hangar telling me that you were going to be a dad. Do you remember how freaked out you were?"

"Yeah." Fitz chuckled at the memory. "But now I think I've got this whole Dad thing figured out."

"You don't sound so sure of that."

"Well, let me ask the expert." Fitz called Eleanor and moments later she ran over to him. She was wearing blue jeans and a white t-shirt that said "Daddy's Little Monkey." Her long brown hair, tied up in a ponytail, looked exactly like her mother's. Fitz knelt down to her level. "Eleanor, I need to ask you a serious question and I want you to tell the truth. Am I doing a good job as a dad?"

She nodded enthusiastically. "You build me fun toys and you read me bedtime stories. And you take me to the zoo to look at the monkeys. And you make me sandwiches, but mommy's are better."

Fitz laughed and gave his daughter a hug. "Thank you, sweetie."

Eleanor kissed her father's cheek, then turned to Mack. "Uncle Mack, is Aunt Yo-Yo going to have the baby soon?"

"We still have about a month to go," Mack answered. "I'll tell you a secret, Eleanor. I'm kinda nervous about being a dad. I think I'll be calling your dad a lot to ask his advice."

Fitz patted Mack's shoulder. "Don't worry, Mack. Believe me, you're going to be awesome."

* * *

 **Thanks for reading! All comments are greatly appreciated.**


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